The present invention relates to a mold for forming composite-material structures without producing strain therein.
Composite materials are being widely used for structural members of aircraft and motor vehicles. Composite-material structures generally require heat and pressure treatment in the forming process. An example of such treatment is an autoclave forming. For fabricating such composite-material structures, a suitable method includes a press-forming method by which forming can be carried out in a short time.
Various press-forming methods have been proposed. For example, a method of fabricating panels is disclosed in Japanese Patent Application Laid-Open Publication No. 62-267,114. A method of integrally forming composite-material structures is disclosed in Japanese Patent Application Laid-Open Publication No. 55-41,210.
The first method of fabricating panels comprises placing a central preformed structure and an outer peripheral preformed structure in a mold, and applying pressure and heat to the structures to form an integral panel. The second method of integrally forming composite-material structures comprises laminating a preformed structure on an elastomer tool, placing the resulting structure in an autoclave, and applying pressure and heat to the structure by utilizing the thermal expansion pressure of the elastomer tool thereby to form an integral structure.
The methods described above, however, are accompanied by the following problems. By the first method of placing a central preformed structure and an outer peripheral structure in a mold, the two structures are fabricated into an integral structure. However, during the forming process, uniform pressure cannot be applied to rising or upstanding portions of the objective structure being formed. By the second method in which an elastomer tool is used, the desired pressure cannot be applied within the required time period. Furthermore, the composite-material structure and the elastomer tool have different thermal expansion coefficient. Consequently, strain is produced in the formed product in some cases.